<title>Fabrication of high-temperature-resistant laser-induced gratings with large refractive index modulation: space-selective precipitation of Ge nanoparticles in glasses</title>

Abstract

High-temperature-resistant laser-induced Bragg gratings were formed in Ge-B-SiO₂ thin glass films fabricated by the plasma enhanced chemical vapor deposition method. Such gratings were induced by exposure of an interference pattern with KrF excimer laser and subsequently annealing at 600°C. The SEM observation of the grating after HF etching revealed that the origin of the grating was the periodic precipitation of crystalline 20 - 40 nm-diameter Ge nanoparticles. Nanoparticles precipitated predominantly in the unirradiated region after laser-induced refractive index change completely erased after annealing up to 500°C. The maximum value of refractive index modulation &#916;<i>n</i> was 6.8 x 10^-3 at 632.8 nm, which corresponds to the &#916;<i>n</i> nearly 10 times as large as that before annealing. A channel waveguide with high-temperature-resistant-grating exhibited high diffraction efficiency and excellent thermal stability.